Sustainability 2011 , 3 1850
Useful information can be obtained by comparing the values of NER and EER for a given process.
Such comparisons illustrate how much of a conversion and extraction process is self-fueled. For example,
in previous studies of oil shale development in the Green River formation of Colorado, Brandt [43,63]
found that EER and NER varied greatly for in situ and mine-and-retort oil shale extraction schemes.
This is because the oil shale extraction processes studied were fueled primarily by the shale inputs to the
retorting process. Similar considerations applied to the largely self-fueled early TEOR operations. These
operations were less energy efficient, but because only produced crude was being consumed, this did not
result in an additional draw on other resources such as natural gas. This self use reduces the endowment
of oil and the net output per unit of capital investment, but will not affect other energy sectors appreciably.
Self use also results in environmental impacts (e.g., GHGs per unit of energy output).
The uncertainty in model results is significant. EROI values actually achieved in the California oil
industry over time are fundamentally unobservable: many of the required data inputs are not publicly
available or were likely even lost over time due to neglect. This lack of data causes fundamental
difficulties in assessing the uncertainty. One conclusion is that this uncertainty is uneven in the above
model functions: detailed operations data are available at the field level in CDC-DOGGR statistics,
while little data are available on technical efficiencies over time. Again, these data were not required to
be reported by regulatory bodies and were therefore never publicly documented.
Despite these uncertainties, this type of analysis has significant value. Because the model relies on
bottom-up data, such as m^3 of water lifted, additional understanding of depletion effects can be generated
compared to top-down EROI assessments based on aggregated economic data. In theory, this allows
diagnosis of the most important effects of depletion, and industry effectiveness in responding to these
depletion impacts.
The global impacts of these forms of depletion on the energy efficiency and environmental impacts
of oil extraction are still poorly understood. At this time of rapid expansion of low-quality oil resources
such as the Canadian tar sands, this is a troublesome gap in knowledge. Given the size and energy
intensity of oil extraction and refining operations, the impacts of such changes on global environmental
impacts are likely large.
Acknowledgements
Charles Hall and Richard Sears provided detailed comments on the methods used here. Bryan Sell
and Jon Freise provided numerous helpful comments on the manuscript, as well as additional data
on drilling energy intensity. Members of the Antique Caterpillar Machinery Owners Club generously
provided historical technical specifications for Caterpillar drill rig engines from the 1950s and 1970s.
Additionally, helpful comments on an earlier version of this work were provided by Tad Patzek, Alex
Farrell and Richard Norgaard at UC Berkeley.